The invention relates to a branch coupling of the type which is used to change the flow of gas between two gas chromatograph capillary columns.
A branch coupling of this type is shown in FIG. 3 of German Pat. No. 26 55 387. In this device, the capillary columns are connected together by a connecting capillary tube. This tube extends from the housing at both sides, and the separation columns are normally slipped onto the ends of the tube. This requires skill and dexterity to avoid damaging the columns and/or the tube. Furthermore, because the connecting tube is relatively long, it has a high flow resistance. As a result, the sample dwells for a relatively long time in the connecting tube, impairing separation in the columns.
This known device also has a cylindrical graphite seal which seals the connecting tube to the center of the housing. The graphite is compressed when the housing parts are screwed together.
Because graphite is used, the seal must be relatively large because it will not withstand high compression. Furthermore, graphite is disadvantageous because it absorbs parts of the gas sample and air and oxygen may diffuse through it.
It would be advantageous to provide a branch coupling which would decrease the flow resistance in the connecting capillary tube, which would reduce or prevent adsorption on seals and in nonflooded dead space, and which would be easier to assemble.